Chris Wilson <ch...@chris-wilson.co.uk> writes:
> In the unlikely case (thank you CI!), we may find ourselves wanting to
> issue a preemption but having no runnable requests left. In this case,
> we set the semaphore before computing the preemption and so must unset
> it before forgetting (or else we leave the machine busywaiting until the
> next request comes along and so likely hang).
>
> v2: Replace readback with only a wmb after asserting the semaphore
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_lrc.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c
> b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 8017efb36f7b..a392186ca40b 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -240,7 +240,8 @@ ring_set_paused(const struct intel_engine_cs *engine, int
> state)
> * until the dword is false.
> */
> engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state;
> - wmb();
> + if (state)
> + wmb();
> }
>
> static inline struct i915_priolist *to_priolist(struct rb_node *rb)
> @@ -1249,6 +1250,8 @@ static void execlists_dequeue(struct intel_engine_cs
> *engine)
> *port = execlists_schedule_in(last, port - execlists->pending);
> memset(port + 1, 0, (last_port - port) * sizeof(*port));
> execlists_submit_ports(engine);
> + } else {
> + ring_set_paused(engine, 0);
> }
> }
>
> --
> 2.20.1
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